The story begins with the backstory of Maui using his magical hook to steal the heart of Te Fiti to give humanity the power of creation, inadvertently releasing the lava demon Te Kā and causing the heart to be lost at sea. Years later, the ocean bestows the heart upon toddler Moana. As vegetation rots on Motunui, Gramma Tala reveals a hidden cavern containing ancient voyaging canoes, confirming their ancestors were navigators. On her deathbed, Tala passes the heart back to Moana, urging her to sail beyond the reef, before her spirit departs as a bioluminescent giant manta ray.
Moana washes ashore on Maui's island, where they form an uneasy alliance. They travel to the realm of monsters (Lalotai) to retrieve Maui's magical fishhook from the giant crab Tamatoa. At the volcanic barrier of Te Fiti, Maui's hook is badly cracked by Te Kā, prompting him to abandon Moana. Heartbroken, Moana asks the ocean to take the heart back, but Gramma Tala's manta spirit empowers her to realize her strength comes from within, leading Moana to retrieve the heart and sail toward Te Kā alone.
Maui returns to provide air cover, shattering his fishhook in the process. Upon reaching Te Fiti, Moana discovers the island is gone and observes a spiral fissure on Te Kā's chest: Te Kā is Te Fiti, transformed into a monster by the theft and trauma of losing her heart. Moana instructs the ocean to part, allowing Te Kā to charge across the dry seabed, where Moana sings to her and restores the heart. Te Kā transforms back into the lush goddess Te Fiti, restores Maui's hook, and gifts Moana a new wayfinding canoe. Moana returns home, where Chief Tui and Sina welcome her, leading their tribe back to the sea as wayfinders.